Process of pulp preparation and product thereof



PROCESS OF PULP PREPARATION AND PRODUCT THEREOF Filed Dec. 5, 1940 w f m u a 0 5 M M 6 W, 4m

04 .0 0 W Y w. w M w 0 0U j QNQMMMNQQNN Patented Jan. 22,- 194e NUNITED sTATEs PATENT OFFICE PROCESS F PULP PREPARATION AND PRODUCT THEREOF David M. Musser and Harry C. Engel, Pittsburgh,I Pa., assignors, by mesne assignments, to Na* tional Cotton Council of America, Memphis, Tenn., a corporation of Tennessee Application December 5, 19.40, Serial No. 368,730

Claims.

u This invention relates to the art of preparing Y b tent lby the lack of satisfactory methods to process these fibers properly for converting them intof bers of desired properties. It is well known that cotton bers resist heating and undergo fibrillation with great difficulty. A comparatively long beating period is therefore necessary to reduce them to suitable neness for paper stock. This long beating time is expensive and tends to slow down mill operations; and has the serious defect that it extensively impairs the utility of the bers by causing transverse breaking of these fibers prior to the splitting incident to fibrillation. Consequently,.the resultant paper product possesses poor folding' and mechanical properties, as compared with a wood pulp` or rag stock that is more easily hydrated.

It has previously been sought to decrease the beating time for such cotton bers through the use of acidic or oxidizing agents or conditions, but fundamental success has not been encountered because the treatments are difficult to control and generally are so `drastic that the iibers are seriously impaired as an incident to reducing v them to the condition at which beating can proceed. u That is, ,such treated cellulosic iibers are permanently damaged, and the paper products are of inferior quality.

Upon investigation, it has beenvfound that eellulosic pulps can be obtained in the manner he'einafter described in order to yield a paper stock superior to those made according to prior art. In particulari t has been found that if the cellulosic pulp is beaten in the presence of a small amount of water-soluble cellulose derivative, suchas methyl cellulose or ethyl cellulose, the beating time is denitely decreased and the paper-making properties of the resulting stock are greatly improved over Athose obtained by prior` processes.

According to the invention, therefore, a mate'- rial is introduced during the beating 'periodfor producing a more rapid iibrillation per unit of beating time, and being further eiective for yielding 'a paper stock superior to the stocks beaten for. a. normal or longer period.

In practicing the invention, the treating agent is introduced to the charged beater at the vstart of the beating process. This agent is introduced preferably in the form of a solution or dispersion in water, but may be employed in a dry or powdery form where a proper condition of beating is established to assure the distribution and opera- 5 tion of the material during the course of the beating period. Thus, if the beating. period is less than 2 hours, the best results appear to be obtained if, for example, methyl cellulose is added in the form of a solution; while if the beating :l0 period is greater than 2 hours, the methyl celluto form a liquor which has the commonly ac-y cepted attributes of a solution.

As an illustration of the extent to which the i beating time may be decreased, a bleachedkraft pulp was subjected to a beating operation in a commercial beater for periods of 1%; hours, in comparison runs where one run included the employment of 6.0 percent of methyl cellulose (based on the weight of dry pulp, and used Aas a 0.3%

solution), while the companion run omitted the methyl cellulose.. The result of such runs is as follows-z "TABLE I c Data'on kraft pulp RunNo. 3o

05 0.5 1. 1.5 1. 0 -eo 0 o .6. 12s 102 111.0 se 74. 4,430 6,270 5,130 0,260 7,580

5s.- 4a.7 57.4 3.6 A

length of a strip of paper, out either in machine f or cross direction, which would break of its own ,weight when suspended vertically; and is a value calculated vfromthe tensile strength and basis vweight of a sheet and isY expressed in meters. 504 Bursting strength is measured by the pressure required to rupture a specimen when tested under the' specied conditions: and the burst factor or v burst is the numerical value obtained by dividing the bursting strength in-grams per square centimeter by the-basis weight o'f the sheet in grams per squaremeter. Tearlng strength is Vmeasured by the force required to tear a specimen under standardized conditions in an instrument designed to simulate in a general way the tearing encountered under use conditions: the tearing fac- -breaking'length after one half hour of beating,

with 6.0 percent of methyl cellulose, is equivalent to the value obtained by beating for 11/2 hours without methyl cellulose, and that a corresponding burst value likewise results. On the other hand, it will also be noted from runs 18 and 20 that the tear value is higher in the methyl cellulose rlmras might be expected from the shorter beating time utilized.

1t has further been found that the concentration and viscosity of the treating material play important roles. For example, it has been found correspondingly greater.

that the high and extra high viscosity types of "A methyl cellulose are more ell'ective than the low and medium viscosity types. That is, for a given weight of methyl cellulose, the high viscosity type expedites beating and enhances the physical properties of the paper to a greater extent than the same weight of the low viscosity type. In making these comparisons, the viscositles of the methyl cellulose were based upon the time required for a denite volume of a2 percent aqueous solution at 20 degrees C. to flow through a standardized Ubbelohde capillary tube. A low viscosity type runs from 20 to 30 centipoises, with an average at 25; a medium type between 40 and 60, with an with an average at 100; and an extra high vis- Acosity type between 250 and 350, with an average average at 50; a high viscosity type at 80 to 120,

hours with 6.0 percent'of methyl cellulose of the specific viscosity (as a 0.3 percent solution).

The proportion of treating material or its effective concentration in the beating liquor deter- -minesjhe physical characteristics of the paper As the beating is continued, these values grad- TABLE m Enect'oj concentration of methyl cellulose Beating,hours.

Concentration percent (based on weight-ofpuip) 0 1.2 6.o' 1z0 vBreakingle11gtl1 Z170 2,990 3,760 Burst...L 15.2 19.0 25.4 35.3

Thus, at a very low relative concentration oi methyl cellulose, a decided improvement in me chanical' properties is effected. At higher concentrations, the percentage increase in properties is The same amount of water was employed in each case, and the solution concentrations of methyl cellulose were 0.06, 0.3, and 0.6 percent.

The flgure of the drawing is a graphic representation of the changes in tear factor, burst fac.

tor, and breaking length, in beating hull liber pulp with 0.3 percent of methyl cellulose in' the beater liquid (calculated at 6 percent onairdry pulp) and without methyl cellulose.

Further, it has been found that. the use of by beating in the presence of methyl cellulose,

over a plain beating as a control, in a given short time, then a similar percentagel of improvement is revealed in a longer time.

Further, it has been found that the beating liquor does not lose all of its methyl cellulose; but

usually about 40 percent of the methyl cellulose taken up by the bers, while about 60 percent of that originally employed is carried forward in the white water discharged during the felting or sheet-forming operation. .This white water can be immediately reused in the next beater run by introduction into the head box'of the paper machine.- preferably with an adjusting of the concentration of methyl cellulose therein. The paper product contains 0.1 to 6 percent of the cellulose ether distributed essentially uniformly throughout the mass of the article. In connection with the acceleration in the production of beating eiects by the present procedure, it may be pointed out that when pulp is undergoing beater action, it will at the start showY low values of breaking length and burst -1'actor.

. ually increase, reach a maximum and then stead- Tsar.: II vEfect of methyl celluloses of diferent vscostes Viscositytype None Low -Medium High Extra high Breakinglength 2.040 asm 2,800 3,720 3,690 summier las 24.1 25.2 ,34.0 35.3 'marmer 5M seo 84.8 88.1 89.5

Using these figures, the following comparison maybe calculated:

. Percent l Percent Average f Average im viseositytype None low and nfxllgg'r high and meggr Y medium blank extra high blank amkingiengzh. r2,o4o 2,855 40 3,705v s2 Burst memles 24.55 50 34.65 im Tcarfsctor 56.4 84.9 5l 88.8 57

ily decrease in volume. Measurement of the drainagetime gives an indication of the change 'of these factors during beating. A standardized procedure exists for this measurement.- When the pulp is underbeaten, the stock is free, shows a low drainage time and drains rapidly on the screens. When the pulp is overbeaten, it has a high drainage time anddrains very slowly; in

f this' overbeaten condition, the pulp requires a slow-running paper-making machine and increased suction.' A highly overbeaten stock 'is practically useless for general paper making because it `drains too slowly and possesses poor paper 2,393,553 properties. It is found, inpractice of this invenample, in Table IV below, the drainage time upto about 8 hours of beating was 10 seconds or less: y

while at 9 hours ot beating, the drainage time had increased to 70 seconds, and further increase occurred later. In the experimental laboratory runs, a Valley type beater was used, with a pulp consistency between 4 and. 5 percent. In a comparative test, it appeared that the experimental beater conditions were such that only half the4 beating time was required as compare'd with a commercial beater.

As a further example of practice, comparison operations were performed with bleached, second cut cotton linters,.both in plain aqueous beat- .ging liquorl and in a; beating liquor containing methyl cellulose. In Table IV below are given the values obtained for a product when a medium viscosity methyl cellulose was employed at 12.0 percent concentration (based on weight of pulp, corresponding t 0.6 percent in the beater liquid), while in Table V the corresponding results are set out for the employment of 6.0 percent of high viscosity methyl cellulose, corresponding to 0.3

percent in the beater liquid.

' TABLE 1V .Data on beating second cut lnters Beating, hours s 7 o i1 Parts of methyl cellulose per 100 parts of pulp 0 12.0 0 12.0 0 12.0 0 12.0 Tear 75.7 90.0 53.6 105.0 38.0 95.5 33.0 82.8 Breaking lengtlLLZO 2,850 1,960 3, 2,010 3,300 2,030 3.870 Burst '13.1 %.3 15.0 20.0 13.2 31,312.9 33.9

Team il [Normlbeating] Beating, hours e 7 s e 'rear n.5 56.4 v5M .o las Breaking length 1,500 1.920 2,040 2,160 2,100 Burst V12.3 14.0 15.5 17.2 13.3

1 Withmethylcellulose) l Beating, hours YMethyl cellulose in liquor,

pei-cent-. 0.3 Y 0.3 0.3 0.3 0.3 Ratio methyl cell ose to pulp -peroent.- 6.0 6.0 6.0 6.0 d0 Amount methyl ce ulose on inishedpaper -.per cent-- 1.64 2.67 2.74 3.03 ear 91.2 88.8 88.4 78.6 72.0 Breakingleligth-. 2,720 3,290 3,700 3,800 .4,220 Burstfactor 24.3 .2 32.3 33.0 33.0

From Table rv. 1t wm bey noted that die average increase in properties obtained by beating the Pulp medium viscosity'methyl cellulose solistion, with four different beating times. correspends to an increase in tear value of 104 percent.

in breaking length of 74 percent, and in vburst value of 122 percent.

In Table Vthe average increase in the test properties when 6.0 percent of, high viscosity methyl cellulose was employed at live diii'erent beating times was found to be an increase of 55 percent in tear factor, 80T percent in breaking length, and 111 percent in burst value.

'I'hese results indicate the effectiveness of the vemployment of such material during a beating of 2030 at the end of 11 hours of beating in plain aqueous solution; while a value of 2 850 is obtained by beating for 5 hours with methyl cellulose solution: thus, the beating time was decreased by more than 6 hours. In T le V,cor responding decreases are indicated;

When it is sought to employ this procedure with other agents in the beatingliquor, care must be observed that these oth'er agents are not in compatible with the action of themethyl cellulose, as ,such an effect tends tooilset the value of the treating material. son, the .behavior of methyl cellulose in association with starch andpaper-makers alum was observed as follows:

Term VI In each instance, the beating time was 1.5 hours, and the raw material was a bleached sulte pulp'. The concentration of methyl cellulose was 2 percent and where starch and alum were employed, a' quantity of 2 percent oi` starch and 'l percent of alum was utilized. From this table,V it will he noted that superior values are obtained by ellfecting the primary beating in the presenceof methyl cellulose'to obtain a proper ber condition, prior to the introduction of starch, alum, or other agents. As a general rule of procedure,

it is desirable that no material be introduced into the beating. liquor priorto an initial action of the methyl cehulose or like 'agent upon the bers,

insofar as such added material may so Amodify the polar properties of the cellulose olf-oiV the. liquor contents as a. whole that adsorption of methyl cellulose on the fibers is diminished. The duration of beating prior to introduction of other furnishes can be determined fromfthe'totalbeating timerequired forthe desired reduction of the stock, and the time required .for incorporating the other iiu'nisdies, butmust be sumclent for" bringing the methyl cellulose to the individual bers' and for at least lthe initiation of nbrilla- As a matter of comparimethyl cellulose isl added in solid form, with commercial rates of beating.

In' particular, it is pointed out that these effects are obtained without the employment of a subsequent heat treatment of such character as to melt and set the methyl cellulose, although heat may be advantageously employed to speed the present procedure may therefore include th'e beating of aqueous suspension in the presence of cellulose ether, followed by the addition"l of sizing, etc., matters a'nd the dilution of the pulp, the forming and draining of the sheets, and the `drying and calendering operations.

As an indication of the increase in fold values as measured by the Seho'pperalester, with diierent runs of treatment in which' methyl cellulose was applied to a, regular sulfite pulp furnish (after starch, size and alum had been introduced into the beater), it was found that foaming .tended to occur: and hence it isfurther indicated to employ the preliminary beating with' methyl cellulose before the other ingredients of the furnish are introduced. However, when the concentration of methyl cellulose is low (such as 0.2 percent), no serious foaming diiiiculty-is to benoted, while the fold values of the'product show deilnite improvement. The foam tends to carry methyl cellulose out of the beater, and hence to reduce the concentration apparently' present.

The feasibility of obtaining extremely high 'fold values, or resistance to separation of iibers by repeated bending along a single line, is indicated by the following:

a .TABLE VII Percent methyl Percent cellulose based methyl eeuu. Prcent {mt- Jm Weight airlose based on i121 edmeln dry Sult pulp beater liquid v l1@ 0- 5 0.025 l 90 1- 0 (l. 050 200 3- 0 0.150 370 4.0 (Lax) 660 5. 0 O. 250 l, 470

water-soluble cellulose ether, due attention being addressed to the lesser solubilities.

The eflect has been obtained with cotton bers including the cotton staple or lint, cotton linters, hull fiber, Aand manufactured cotton in .which oxycellulose may have been formed; and also in sulfate, sulflte .and soda pulps', in jute, manila hemp, and flax bers.- It thus is applicable genton bers in raw condition or after subjection to chemical treatments, ,suoli as kier boiling or bleaching, in which the integrity of the fibers has been retained and they are in condition for fibrillation. A

'I'he exact behavior of the eilective' compounds in lowering the beating time is not entirely clear. However, it may be pointed out that two prodesses occur inthe beater: one being the cutting action by which the lengths of the bers are reduced, and the other being the fibrillation or the longitudinal sputun'g of the chers. The meer action is obtained by beating a long time with very little pressure on the beater rolls, and is the l0 preferred one because it gives a ilne-bodied feltup the drying of the-paper sheets, as in the usual commercial practice.` The making of paper by able stock with long ber lengths. The action lof methyl cellulose and like materials appears to be effective in decreasing the beating time and in improving the mechanical properties of the resulting paper product, by facilitating iibrillation (possibly by catalytic action) and in assuring a cementing of4 the'brils during the sheet-forming operation.

' It is obvious that the invention may be prac- \ticed in many ways other than those set out the felted product of beating a brous cotton celluloslc material in aqueous suspension with a high viscosity water-soluble methyl cellulose, and characterized in containing at least substantially 2.4 percent of methyl cellulose and in having a tear factor in excess of 70, a breaking length in excess of`2500, and a burst strength in excess of 25.

2. The method of'producing a sized feltable pulp from ilbrous celluloslc materials, which in cludes the steps of beating the fibrous material in an aqueous suspension ,containing water-soluble methyl cellulose at least until iibrillation vbegins, thereafter adding a starch and alum siz-V ing material, and continuing the beating opera- 4 0 tion until felting qualities are developed.

3. Themethod of producing sheets of felte brous celluloslc materials. which includes thestep of beating the brous material in an aqueous /solution whose solute essentially consists of substantially 0.3 percent methyl cellulose, with the solution present vin the substantial quantity of 6.0 percent of water-soluble methyl cellulose by weight of air-dry pulp.

4. The methodof producing strong sheets of fibrous celluloslc materials, which comprises beating the fibrous material in an aqueous solu-l tion whose solute consists essentially of watermaterial.

5. The method of producing paper sheets from fibrous celluloslc materials, Awhich includes thev steps of beating the fibrous materials in an aqueous solution whosev solute consists essentially of 0.06 to 0.6 percent of water-soluble methyl cellulose of viscosity `over centipoises, lmtil felting Aqualities are developed,`and thereaftenformerally to cellulosic ber materials, including cot- ,65 ing the sheet wfhne retaining *methyl cenmose therein. y DAVID HARRY C. mmm 

